Free piston engine



March 26, 1963 s. s. SPIRES ETAL 3,082,754

FREE PISTON ENGINE Filed Sept. 2, 1960 4 Sheets-Sheet 1 66 M57 A? 1' 1. 66 59 w 13 IN V EN TORJ By W 6% g/ffarrze .5

March 26, 1 963 s. s. SPIRES E-TAL FREE PisToN ENGINE 4 Sheets-Sheet 2 Filed Sept. 2, 1960 INVENTORJ Sam/sud. 62 124-25 eommua bf A/OWELL March 26, 1963 s. s. SPIRES ETAL FREE PISTON ENGINE Filed Sept. 2, 1960 4 Sheets-Sheet 3 INVENTORS 5122,95 6. 5 /255 BY iawzawo H A/on'A'LL MW 3 EN ww United States Patent 3,082,754 FREE PISTON ENGINE Stephen S. Spires, 6034 Coldwater Canyon Ave., North Hollywood, Calif and Rowland H. Nowell, 5551 /2 Costello Ave., Van Nuys, Calif.

Filed Sept. 2, 1960, Ser. No. 53,831 14 Claims. (Cl. 123-46) The present invention relates generally to free piston engines. More particularly, the invention relates to a lightweight, multi-cylinder, air receiver pressure controlled and air-cooled gasifier, but it will be apparent to those skilled in this art that various aspects of the invention may be utilized in connection with compressors, or heavy duty engines, or with other piston engines.

Although free piston engines have not come into widespread commercial use, their general organization and mode of operation is understood. A rather broad summary of the history, development and current state of the art of this engine type is recorded in the publication Consulting Engineer, issue of August 1953. The theoret-ical superiority of the free piston type is recognized and it is one of the objects of this invention to satisfy a recognized need for a commercially feasible free piston gasifier of reduced size and weight. The invention is thus adapted for use as a mobile engine and also adapted to use in multiples for driving a receiver common to a plurality of the units.

It is also among the objects of our invention to provide a free piston gasifier having a very wide power output operating range and particularly to provide high torque at low speed, for a receiver such as a turbine.

Another important object of the invention is to provide a free piston engine having an improved service life. For this purpose we have provided means to insure the delivery of lubricating and coolant medium instantaneously with the starting of the engine and reliably continuing throughout the period of operation of the engine.

Another object of the invention is to provide a multicylinder free-piston organization for reducing the size and Weight of the unit per cylinder and in which the cycles of the separate cylinders are synchronously controlled.

Another important object is to control pressures in the air receiver to extend engine operating range, and to insure greater economy plus greater efiiciency at part load.

Yet another important object of the invention is to provide a greatly improved free piston engine configuration, for commercial production of a twin-cylinder, aircooled free-piston engine. To this end, we have devised an engine with a greatly reduced number of parts, simple in design and adapted for a very long service life. As a result, maintenance has been greatly simplified and a substantial reduction in the ratio of weight to horsepower has been achieved. This engine configuration comprises an easily assembled organization of parts and the assembly is integrated by fastening means which retain the desired organization of parts despite high thermal stresses induced by combustion during operation of the engine.

The foregoing and other objects and advantages of our invention will be apparent from the following description of a presently preferred embodiment thereof,

ice

when taken in conjunction with the annexed drawings wherein:

FIGURE 1 is a top plan view of a light-Weighttwincylinder, air-cooled gasifier constructed in accordance with our invent-ion;

FIGURE 2 is a side elevational view;

FIGURE 3 is a transverse sectional view taken sub stantially on the line 3-3 of FIGURE 2;

FIGURE 4 is an end elevational view;

FIGURE 5 is a horizontal sectional view taken substantially on the line 55 of FIGURE 2;

FIGURE 5a is a vertical sectional view along the axis of one of the pistons, on an enlarged scale, of a pump means incorporated in the pistons of the engine for providing a flow of lubricating and cooling medium; and

FIGURE 6 is a largely schematic view of the engine and a portion of the associated control mechanism.

Referring to the drawings for the general arrangement of the invention and in particular to FIGURE 6, the engine block assembly comprises a pair of combustion cylinders 10 and 11, a pair of compression cylinder blocks 12 and a pair of cylinder heads 13. The combustion cylinders 10 and 11 are substantially identical to one another as are the compression cylinder blocks 12 and cylinder heads 13. However, the combustion cylinders are difierently identified, numerically, for convenience in subsequently describing the mode of operation of the engine.

Each of the combustion cylinders 10 and 11 has a pair of countermoving free pistons 14, each having a power piston portion 14a and a compressor piston portion 14b. The pistons 14 are of a one-piece construction and are hollow, having an axial bore which is blind at the inner end. A pair of piston guides 15 is affixed to each cylinder head 13, coaxially with the associated combustion cylinder 10 or 11. Each of these extends inwardly into one of a pair of compressor cylinder bores of the block 12 to reciprocably slidably support the outer end of an associated piston 14. A pump means is incorporated within each guide 15 and piston 14 to circulate cooling and lubricating oil.

Each compressor cylinder block 12 has an air receiver or accumulator chamber 16, of variable volume, and this pair of chambers has fluid intercommunication by a means 17 whereby the pressure of the two chambers remains substantially equal. Each bore of each compressor cylinder block 12 in which a compressor piston 14b reciprocates is divided by the piston into two dependently variable bounce and compressor chambers 18 and 19 respectively. As a piston 14 moves outwardly, in response to combustion within the cylinder 10 or 11, air is compressed behind the compressor piston 14b in the bounce chamber 18. Simultaneously, one-way inlet valve means 20 opens to the chamber 19 whereby air at substantially atmospheric pressure is drawn into the expanding chamber 19. At the outer dead position of the compressor piston 14b, the air compressed in the chamber 18 provides the force for returning the pistons 14 inwardly towards inner dead position. Upon the return stroke the inlet valve means 20 is closed and another one-way delivery valve means 21, dividing the air receiver chamber 16 from the compressor cylinder bore opens to pass air from the decreasing volume chamber 19 into the air receiver chamber.

At the outer dead position of a pair of pistons 14, compressed supercharging air is admitted from one air receiver chamber 16 into one of the combustion cylinders or 11 through inlet ports 22. The incoming air aids in unifiow scavenging the products of combustion from the combustion chambers through ports of an exhaust manifold 23', around each combustion cylinder 10 and 11, for ultimate delivery to a receiver such as a turbine through a manifold exhaust 23a. The exhaust manifolds 23 are located more closely towards the center of the combustion chambers than are the inlet ports 22 and complete scavenging is assured by an excess of supercharging pressure over combustion chamber pressure.

The pair of pistons 14 in each of the combustion cylinders 10 and 11 is synchronized for opposite inward and outward movement through a mechanical drive means which is also synchronously associated with a fuel injector mechanism for the cylinder. The stroke length and frequency of a pair of pistons 14 is determined, in part, by the pressure of the air in the bounce chambers 18 and in order toequalize the pressures in the bounce chambers for each of the combustion cylinders 10 and 11, the pairs of bounce chambers have fluid communication through a means 24. The air receiver chamber 16, in addition to providing supercharging air for the combustion cylinders 10 and 11, also provide a selectively controllable source of air for varying the pressure in the bounce chambers, thus contributing to the control of engine speed and power output.

The bounce chamber pressure control takes the form of a restrictor means 25, responsive to pressures in the chambers 16 and pressures in the bounce chambers 18, when the compressor pistons 1415 are in their inner dead positions. The restrictor means includes a housing 26 for a diaphragm 27. The interior of the housing 26 on one side of the diaphragm 27 has communication with the pair of bounce chambers 18 for each cylinder 10 or '11. The other side of the diaphragm is drivingly connected to a valve member 29 that controls and normally prevents the flow of compressed air from the air receiver chambers 16 to alternate pairs of the bounce chambers, 18, as for example between the conduit means 17 and 24. A check valve is interposed between the valve 29 and conduit means 17 for preventing a reverse flow of air into the air receiver chamber 16, but air can be relieved from the bounce chambers 18 through a vent 31 to the atmosphere.

The valve 29 normally closes the conduit'means 24 to both the vent 31 and the conduit means 17. The valve 29 is movable to alternatively establish communication of the conduit means 24 and either the vent 31 or conduit means 17 by a control member 32 having a yieldable connection with the valve through a spring 33. The position of the valve 29 viu'th respect to the ports from the means 17, means 24 and vent 31 is accordingly a function of the positions of the diaphragm 27 and control member 32. The position of the control member 32, depicted physically in FIGURES 1, 2, 3 and 4 of the drawings, may be adjusted either manually by the operator of the engine or by any other desired form of controlled actuating means. When it is desired to increase bounce chamber pressure, thereby increasing the frequency of the pistons 14, the control member 32 is actuated until the valve 29 assumes the position shown in FIGURE 6, against the air pressure on the other side of the diaphragm. Air pressure in the air receiver chambers 16 then overrides the check valve 30 and passes into the conduit means 24, the vent 31 now being closed by the valve 29. When pressure in the bounce chambers 18 has increased sufii-- ciently to move the diaphragm 27 and valve 29 to the left, the port from the means 17 is closed by the valve, concurrently with closing of the port to the means 24.

When it is desired to decrease the frequency of the pistons 14, the control member 32 is moved to the left. The valve 29 is then permitted to move to the left to establish communication between the vent 31 and means 24. As a result, air bleeds out of the bounce chambers 18 until the air pressure on the diaphragm 27 counterbalances the pressure exerted by the control member 32 and spring 33. The control valve 29 then returns to position for closing the vent 31.

More specifically, and referring now to FIGURE 5, it will be seen that the engine block assembly is extremely simplified, involving pairs of substantially identical parts. Furthermore, the parts are held in assembled relationship in a manner to avoid stresses which might otherwise be induced due to expansion under heat. As a result of this engine configuration, efiicient cooling by air is achieved.

The combustion cylinders 10 and 11 have integral radial cooling fins 46 that extend almost entirely around the combustion chamber portion. As can be seen from FIG- URE 3, the cooling fins are interrupted on the confronting sides of the pair of combustion cylinders 10 and 1%, in order to leave room between the cylinders for mounting a portion of the engines control mechanism. Referring now to FIGURE 5, it is to be noted that the cooling fins 40 are spaced apart axially of the combustion cylinder in the space between the exhaust manifold 23 and a mounting flange 41.

Each of the compressor cylinder blocks 12 spans the entire Width of the engine and is formed with a parallel pair of compressor cylinder bores 42 that are coaxially aligned with the pair of combustion cylinders 10 and 11, when the engine is finally assembled. At their inner ends, the bores 42 are counterbored, as indicated at 43, to provide an outwardly facing shoulder on which the one-way delivery valve means 2 1 can be mounted to control the passage of air into the air receiver chambers 16. The one-Way delivery valve means 21 may take the form of a ring of one-Way reed type valves. The outer edge of the valve assembly is seated against the shoulder of the counterbore 43 and the inner edge is secured to an end of one of the combustion cylinders 10 or 11.

The air receiver chamber 16 is defined in each compressor cylinder block'lZ, inwardly of the counterbore 43, between the one-way delivery valve means 21 and an end wall 44. On one side of the engine, this end wall of the block 12 is provided with an opening 45 that receivestheexhaust end portion of one of the cylinders 10 or 11 to hold that end of the cylinder in coaxial alignment with the compressor bore 42 on that side of the engine, as canbe seen from FIGURE 5, for example, in connection with the lower combustion cylinder 11. The exhaust end of the cylinder is pushed into the bore or opening 45 until an exterior shoulder of the exhaust manifold 23 abuts on a circular gasket 46 on a confronting shoulder of the end wall 44.

The other side of each compressor cylinder block 12 has a somewhat frusto-conically shaped extension 47 of the end wall of the air receiver chamber 16, which receives the intake end portion of one of the combustion cylinders 10'or 11. The inlet ports 22 of the combustion cylinders are thus disposed to cyclically receive compressed air from the air receiver chambers, in response to the valving action of the power piston portion of one of the pistons 14. A gasket 48 is mounted between confronting faces of the mounting flange 41 of the combustion cylinders 10 and 11 and the end of the extension 47. A plurality of bolts or studs 49 are passed through the mounting flange and into the extension to provide the sole fastening means interconnecting each cylinder 10 or 11 to one of the compressor cylinder blocks 12. This feature of single plane attachment permits expansion and contraction to occur in the combustion cylinders 18 and 11 without imposing any undue thermal stresses on the combustion cylinders or the compressor cylinder blocks 12.

In order to provide inlet manifolds, each compressor cylinder block has a substantially rectangular cavity formed on both its upper and lower faces, like the cavity 50, a portion of which is shown in FIGURE 3. As is shown in FIGURE 5, a passage 51 extends vertically through the wall separating the two compressor cylinder bores 42 of each compressor cylinder block to intercommunicate these two cavities so as to define one inlet manifold. The cavity 50 on the lower face of each compressor cylinder block is covered by a plate 52 and a plate 53 covers the cavity of the upper face of the block. An air cleaner 54 for incoming air is mounted on each top cover plate 53 and conducts air into the inlet manifold defined by the upper cavity of the associated block, the vertical passage 51 and the lower cavity 50.

It will be noted that there is a clearance space between each compressor piston 14b and the one-way delivery valve means 21, when the compressor piston is in inner dead position. Each compressor cylinder bore 42, in the area of this clearance space, is formed with a pair of diametrically opposite, circumferentially disposed narrow slots 55 (see FIGURE 3) over whose outer end the one-way inlet valve means 20 is mounted within the cavity 50. This one-way inlet valve means preferably comprises a reed type valve, like the one-way delivery valve means 21, and acts to cyclically permit air to be drawn from the inlet manifold into the compressor chamber 19, during the combustion stroke of the associated piston 14.

The compressor cylinder blocks 12 have an increased wall thickness around the air receiver chambers 16 and opposite pairs of horizontally extending parallel tie rods 56 are passed through suitable aligned openings formed in these wall portions on opposite sides of the engine. As shown in FIGURE 2, the exposed opposite ends of these tie rods are threaded and extend in the direction of the cylinder heads 13. Suitable fastener means 57 are secured to the threaded ends of the tie rods 56, with the fastener set to a predetermined torque limit in order to avoid inducing excessive axially compressive stresses in the cold engine assembly.

The use of the tie rods 56 in this fashion serves to provide a rigid assembly of the combustion cylinders and 11 and compressor cylinder blocks 12 but without inhibiting axial expansion of the combustion cylinders when they are hot. Referring once again to FIGURE 5, it will be recalled that the pairs of gaskets 46 and 48 are interposed between the compressor cylinder blocks 12 and the opposite abutments of each combustion cylinder. It will be understood that these gaskets are compressed to define fluid seals when the engine is cold, due to the torque fit of the fasteners 57 on the tie rods 56. When the engine is hot, these gaskets are further compressed by the axial expansion of the combustion cylinders 10 and 11, this expansion occurring in axially opposite directions relative to the single plane attachment at the flange 41 of each combustion cylinder. It will be appreciated that the ultimate axial expansion which can occur is limited by the opposite abutments provided by the pairs of fastener means 57 of each tie rod 56. This part of the engine block assembly is thus held together against the very high combustion pressures of the combustion cylinders 10 and 11 by the tie rods 56, which also reinforce this subassembly against torsional, bending and axial expansion forces.

The pair of cylinder heads 13 have a profile shown in FIGURE 4, similar to the profile of a mounting flange 58 formed at the outer end of each compressor cylinder block 12. A gasket 59 is interposed between the abutting faces of the flange 58 and head 13 and the head is secured in place by a plurality of suitably located fas.

teners 66. Each cylinder head 13 is also formed with a plurality of horizontally extending cooling fins 65.

As is shown in FIGURE 5, each cylinder head 13 is formed with a pair of openings 60 that are disposed coaxially with the combustion cylinders 10 and 11, in order to receive the piston support and guide members 15. Each of these members has an integral flange 61 for seating on the outer face of the cylinder head 13 and a gasket 62 is interposed between the confronting faces of the cylinder head and flange 61 to provide a fluid-tight seal when suitable fasteners 63 are secured in the cylinder head and flange. A tubular portion 64 of the member 15 is thus rigidly supported coaxially within the asso ciated compressor cylinder bore 42 and extends inwardly beyond the plane of the one-Way delivery valve means 21. Each of the pistons 14 has an axially extending blind bore 70 that is telescopically slidable over the tubular portion 64 of the corresponding member 15. As is shown in FIGURE 5, the piston skirt is of a wall thickness which is slidable through the annulus defined between the exterior of the tubular portion 64 of the support member and the interior of the combustion cylinder 10* or 11, as the case may be. Since the tubular portion 64 of the member 15 extends inwardly into the confronting end of the associated combustion cylinder, the piston 14 and the support member 15 firmly support one another throughout the range of reciprocation of the piston.

To provide a fluid seal between the dependently variable chambers 13 and 19, the compressor piston portion 14b is provided with a self-lubricating compression ring '71 in a suitable groove formed in the periphery of the compressor piston. Similarly, the head of the power pis ton portion 14a mounts a plurality of compression rings '72 and an oil or wiper ring 73. In order to facilitate the mounting of the compression rings '72 and oil ring 73 in their grooves, both ends of the combustion cylinders 10 and 11 are flared, as indicated at 74, to force the rings radially inwardly into their grooves when the piston 14 is slipped into (the end of the combustion cylinder.

A mechanical means is provided to synchronize the movement of all pistons of the engine. As is shown in FIGURE 5, each compressor piston 14b has one end of a synchronizer arm connected thereto. Of the two compressor pistons 14b for each combustion cylinder 19 or 11, one of the synchronizer arms is positioned above the horizontal median plane of the cylinder while the other is positioned below this median plane. Thus, referring to the pair of pistons in the combustion cylinder 11, a synchronizer arm 75 connected to the right hand compressor piston 14b is spaced beneath the plane of the figure and extends in an axially inward direction through a suitable bore that extends through a thickened wall portion 77 of the air receiver chamber 16. -A synchronizer arm '76 of the left hand compressor piston 14b is above the plane of FIGURE 5 and also extends inwardly through a suitable bore in another thickened wall portion within the air receiver chamber 16.

A substantially rectangular open-top box 78 is supported on engine accessory brackets 79 in the space between the combustion cylinders 10 and 11. A bearing box 80 is supported within the box 78 and rotatably mounts a pair of pinions 81. Referring to FIGURE 3, it will be seen that the innermost ends of the synchonizer arms 75 and 76 are formed with gear teeth for driving engagement with opposite sides of these pinions. The pistons 14 of each combustion cylinder 10 or 11 are accordingly phased for concurrent opposite movement, synchronously moving between outer dead positions and inner dead positions.

The cycles of the combustion cylinders 10 and 11 are also synchronized through the medium of the synchonizer arms 75 and 76 and the pinions 81. The pair of pinions 81 have driving engagement with a common shaft in the bearing box 80 and therefore simultaneously move in the same direction, either clockwise or counterclockwise. It will be recalled that each synchronizer arm 75 has tangential driving engagement with a lower side of one of the pistons 81 while each of the synchronizer arms 76 has tangential driving engagement with an upper side of one of the pinions 81. Referring to FIGURE 5 and assuming that the pistons 14 in the combustion cylinder 11 are moving inwardly towards inner dead position, the

pinions 81 will both move in clockwise direction as viewed from the bottom of the figure. The left hand piston 14 of the combustion cylinder 10 has its synchronizer arm drivingly engaged with the bottom of its associated pinion 81 and will therefore be moved to the left. The right hand piston 14 of the combustion cylinder 10 has its synchronizer arm '76 drivingly engaged with the top of its associated pinion S1 and therefore will also be moved outwardly towards outer dead position.

The rack and pinion means just described not only serves to synchronize all of the pistons, but also serves to cyclically inject fuel into the combustion chambers. Referring to FIGURE 3, it will be seen that a cover plate 84 for the accessory box 78 supports a pair of fuel injector pumps 35. The upper synchronizer arms '76 on their upper faces are formed with linear cams 86 onto which a roller 87 of a pump actuating arm 88 is biased by a means in the pump. Each pump has a conduit 89' leading from its outlet to an injector spray nozzle 90 and each nozzle is mounted on a pad 91 formed in the corresponding combustion cylinder 10 or 11, at a position corresponding to the center of the combustion chamber. It will of course be understood that the linear cams 86 are adapted to actuate the pumps 85 for causing a charge of fuel to be injected by the nozzles 90 as the pistons 14 approach inner dead position.

The mean temperature of the engine scavenging air 950 F. and the gas temperature may approach 1450 F. and 3000 p.s.i.g. at maximum engine output. It will be appreciated that the heads of the power piston portions 14a cannot have a very long service life under such adverse thermal conditions unless properly lubricated and cooled. Therefore we have devised a means for pumping a lubricating and cooling medium which takes advantage of the reciprocation of the pistons 14 on the piston guides 15, to insure continuous recirculation of the lubricant coolant, and also to insure that the lubrication will take place immediately upon starting of the engine.

The pump means is best seen in FIGURE a. Each piston guide 15, at its fixed end, has a coaxial bore 95 which is tapped at its outer end to threadedly receive a fitting 96, through which oil is supplied. The piston guide '15 is also formed with an axially extending oil return passage 97 that extends through the wall of the tubular portion 64 of the piston guide. At its inner end, the return passage 97 communicates with the interior of the tubular portion 64, just behind a plurality of seal rings 98 mounted on the exterior of the guide near its free end. The outer end of the return passage 97 is also tapped to threadedly seat another fitting 99.

Referring briefly to FIGURE 4, it will be seen that the two oil supply fittings 96 are intereom municated by suitable lines 100 to a T 101, which in turn is communicated to a source of oil (not shown) by another conduit 102. Similarly, the oil return fittings 99 are intercomnmnicated by conduits 103 to a T 104, which in turn is communicated to the source of oil by another conduit 105. It is to be understood that the external supply of oil is provided with a means for cooling the recirculating supply of oil.

Referring again to FIGURE 5a, the domed head of the power piston pontion 14a is interiorly provided with a rearwardly extending coaxial boss 106. This boss is smaller than the surrounding skirt portion of the power piston but the piston head is formed with integral ribs 107 disposed radially between the boss 1% and the surrounding skirt. The boss 106 is also formed with a coaxial bore 108 and a plurality of orifices 109 extend radially outwardly from this bore to the exterior of the power piston portion 14a, through the ribs 107. The orifices 109 are adapted to provide metered amounts of oil for lubricating purposes to the exterior of power piston portion 14a in the circumferential area between the wiper ring 73 and the adjacent compression ring 72.

Referring briefly to FIGURE 5, it will be noted that the boss 106 of each power piston head also has an 8 orifice 110 extending radially outwardly from the bore 108 to the space within the skirt of the piston and between the radial ribs 107. Thus a portion of the oil delivered to the bore 108, by the pump means presently to be described, is diverted for cooling purposes.

Referring again to FIGURE 5a, the piston head bore 108 is adapted to seat a spring loaded Washer 112. A hollow piston rod 113 is coaxially held in place in the piston head bore 108 by means of a bolt 114, this bolt being provided with a coaxial bore 115 for delivering oil to the inner end of the piston head bore 108. The other end of the hollow piston rod 113 is supported for slidable reciprocation within the tubular portion 64 of the piston guide by an oil piston 116, which takes the form of a cap threadedly engaged with the exterior of the piston rod. The piston 116 is provided with an exterior circumferentially extending seal ring 117 to prevent the passage of any substantial amount of oil to opposite sides of the piston during reciprocation.

The hollow piston rod 113 contains a pair of tubular plungers 1 18 and 119 held apart by a compressed coil spring 120. The plunger 119 has one end thus spring biased against a seat 121 formed on the inner face of the nose of the oil piston 116. The piston nose is formed wtih a plurality of ports 122 which provide fluid communication between the exterior of the piston 116 and an annulus 123 defined between the interior of the tubular piston rod 113 and the exterior of the plunger 119. The plunger 119 has an integral circumferentially extending enlargement at 124 in sliding engagement with the interior of the hollow piston rod.

A butterfly valve 128 is mounted at the inner end of the oil inlet bore 95. When the compressor piston portion 14]) moves towards inner dead center position on its compression stroke, the hollow piston rod 113 is also pulled in the same direction. Since the plunger 119 is held in closed position against the valve seat 121, the movement of the oil piston 116 away from the butterfly valve 128 causes the valve to open and oil to be drawn into the enlarging pump chamber space between the oil piston and the valve. On the combustion stroke of the free piston 14, the butterfly valve 128 is closed whereby the oil pressure exerted on the rear face of the enlargement 124 of the plunger 119, causes compression of the spring and lifting of the plunger 119 away from the valve seat 121. The oil in the pump chamber is then permitted to pass into the tubular plunger 119 for forceful delivery through the hollow piston rod 113 and for discharge through the other end of the piston rod. When the piston 14 reaches the outer dead position shown in FIGURE 5a, the tubular plunger 119 is once again urged into closed position on the seat 121, as the force of the spring 120 overcomes the diminishing pressure of the oil in the pump chamber.

The other tubular plunger 118, in about its midportion, is formed with a plurality of radially extending ports 130 that lead to a circumferentially extending groove 131, formed in the exterior of the plunger. The hollow piston rod 113, in the portion around the groove 131, is formed with a plurality of orifices 132 extending forwardly and radially outwardly from this groove to be aimed at the spaces in the piston head between the radially disposed ribs 107. Thus, on the combustion stroke of the piston 14, when the tubular plunger 119 is open, the oil delivered from the pump chamber is delivered through the hollow plungers 119 and 118 and the hollow piston rod 113 to be forcefully sprayed out of the orifice 132 for cooling the piston head. Some of the oil is also forced through the bore 115 in the bolt 114 to be delivered from the piston head bore 108 through the orifices 109 for lubrication.

It will be recalled that the orifices 109 are adapted to deliver relatively small metered amounts of lubricating oil. The amount of lubricating oil which is delivered is, of course, not recovered but is burned along with the 9 fuel, the products of combustion being scavenged through the exhaust manifold. The oil used for cooling, i.e., the oil delivered by the orifices 132 and the oil relieved through orifice 110 is recovered through the 'oil return passage 97.

The tubular plunger 1 19 also acts as a relief valve. Thus, if excessive oil pressure is built up in the pump chamber on the compression stroke of the piston 14, the spring 120 is compressed more than usual by the excessive oil pressure on the rear face of the enlargement 124 of the plunger 119. The plunger is thus moved farther away than usual from the valve seat 121 until the enlargement 124 moves past a plurality of radial ports 133 formed in the hollow piston rod 113. When this occurs, oil in the annular space 123, rearwardly of the enlargement 124, can escape through the ports 133 into the annular space between the piston rod 113 and the hollow portion 64 of the piston guide 15, to escape through the return passage 97.

Referring to FIGURE 6, it will be recalled that the engine includes means for varying the pressure in the bounce chambers 18. This control means includes the conduit means 24 for sensing bounce chamber pressure. As is shown in FIG. 5a, each piston guide 15 is formed with an axially extending passage 135 that is tapped at its outer end to receive a fitting 136 communicating with the means 24. The passage 135 extends inwardly through the wall of the tubular portion 64 of the piston guide 15 and terminates in a radially outwardly opening port 137. As is shown in FIGURE 6, the port 137 of each piston guide is positioned to be open, in response to valving action of the reciprocating piston 14, only while the piston is in the reversing phase at inner dead position. Thus the pressure of the bounce chambers 18 is sensed, and the restrictor means '25 is actuated if necessary, while the pistons 14 pass through inner dead positions.

In addition to the restrictor means 25 for increasing or decreasing bounce chamber pressure, the engine also has a means to vary the volumes of the air receiver chambers 16 as a function of selected engine output. As a result, the extent of supercharging depends upon the demands made upon the engine and a substantially uniform supercharging pressure of air entering the combustion cylinders through the ports 22 is also achieved. Referring to FIGURE 5, it will be seen that each compressor cylinder block 12, on the side having the extension 47, is formed with a piston chamber 140. The outer end of this piston chamber is closed by a cover plate 141 that is secured in place by suitable fasteners 142. At its inner end, the piston chamber 140 is provided with an outwardly facing shoulder 143 for limiting inward movement of a piston 144 in the corresponding air receiver chamber 16, by engaging a complementary flange 145 of the piston. To prevent the escape of supercharged air from the air receiver chamber 16, the piston flange 145 is adapted to seat a seal 146. The piston 144 is hollow and interio-rly seats one end of a compression spring 147 Whose other end is seated on the inner face of the cover plate 141. A vent 148 is formed in the cover plate 141 and the position of the piston 144 is thus a function of the pressure of the air in the air receiver chamber 16 and the combined pressure of the spring 147 and atmospheric pressure.

While a presently preferred embodiment of our free piston engine has been illustrated and described herein, it is to be understood that we do not wish to be limited to the various details of construction hereinbefore set forth but only by the spirit and scope of the following claims.

We claim:

1. In an internal combustion engine: a combustion cylinder, a pair of compressor cylinders coaxially disposed at opposite ends of said combustion cylinder; a pair of free pistons mounted in said combustion cylinder for opposed reciprocation, each of said pistons having a compressor piston portion reciprocable in the associated compressor cylinder and dividing the associated compressor cylinder into dependently variable compressor and bounce chambers; means to cyclically equalize fluid pressures in the pair of bounce chambers of said combustion cylinder; and means including said compressor chambers for cyclically ingesting fluid compressed in said compressor chambers into said combustion cylinder.

2. In an internal combustion engine: a pair of combustion cylinders; a pair of compressor cylinders coaxially disposed at opposite ends of each of said combustion cylinders; a pair of countermoving free pistons mounted in each of said combustion cylinders, each of said pistons having a compressor piston portion reciprocable in the associated compressor cylinder and dividing the associated compressor cylinder into dependently 'variable compressor and bounce chambers; accumulator means to cyclically receive pressurized fluid from said compressor chambers for cyclic delivery to said combustion cylinders; and selectively controllable means to vary the frequency of said pistons by increasing and decreasing fluid pressures in said bounce chambers, said selec tively controllable means including means to intercommunicate said bounce chambers with said accumulator means for an increase in bounce chamber pressure and means to vent said bounce chambers to the atmosphere for a decrease in bounce chamber pressure.

3. The internal combustion engine of claim 2, wherein said selectively controllable means to vary the frequency of said pistons comprises: a housing; a diaphragm in said housing; a valve member having one end drivingly connected to one side of said diaphragm, said valve memher having portions of varied cross-sectional area along its length; a control member yieldingly connected to the end of said valve member remote from that connected to said diaphragm; first conduit means for communicating fluid pressure from said bounce chamber with the side of said diaphragm opposite that connected to said valve member; second conduit means for communicating said bounce chamber pressure with a first portion of said -valve member; third conduit means for communicating the fluid pressure from said accumulator means with a second portion of said valve member; and fourth conduit means communicating atmospheric pressure with a third portion of said valve member, whereby said valve member selectively communicates said second conduit means with said third conduit means or said fourth conduit means in accordance with said bounce chamber fluid pressure and the position of said control member.

4. In an internal combustion engine: a pair of parallel combustion cylinders; a pair of compressor cylinders coaxially disposed at opposite ends of each of said combustion cylinders, each of said compressor cylinders being adjacently parallel to a compressor cylinder of the other pair of said compressor cylinders; a pair of countermoving free piston mounted in each of said combustion cylinders, each of said pistons having a compressor piston portion reciprocable in the associated compressor cylinder and dividing the associated compressor cylinder into dependently variable compressor and bounce chambers; a pair of air receiver chambers, each of which is adjacent a parallel pair of said compressor cylinders and adapted to cyclically deliver fluid under pressure to one of said combustion cylinders; means for each of said air receiver chambers to cyclically pass compressed fluid from the compressor chambers of a parallel pair of said compressor cylinders into said air receiver chamber; and means to cyclically equalize fluid pressures in the coaxial pair of bounce chambers of each combustion cylinder only while said pistons of said combustion cylinder pass through inner dead positions.

5. An internal combustion engine as set forth in claim 4 in which each of said air receiver chambers has a means for varying the volume of said air receiver chamber as a function of air receiver chamber pressure and atmospheric pressure.

6. An internal combustion engine as set forth in claim in which said means for varying the volume of said air receiver chamber includes a movable wall biased for movement in a direction to decrease the volume of said air receiver chamber and yieldably resisting expansion of said air receiver chamber, the side of said movable wall remote from said air receiver chamber being vented to the atmosphere.

7. In an internal combustion engine: a pair of parallel combustion cylinders; a pair of compressor cylinder blocks each of which receives an end of both said cornbustion cylinders and each of which is internally divided into an air receiver chamber and a parallel pair of compressor cylinders coaxial with said pair of combustion cylinders, each of said air receiver chambers having a portion, on one side of said block, coaxial with one of said pair of compressor cylinders of the same block, surrounding a plurality of inlet ports formed in an inlet end portion of one of said combustion cylinders, said combustion cylinders each having an exhaust manifold, surrounding a plurality of exhaust ports formed in the other end portion of said combustion cylinder, and said exhaust manifold being contiguous to the other side of one of said blocks; fastening means rigidly securing one end only of one of said pair of combustion cylinders to one only of said pair of blocks and securing the opposite end only of said other of said pair of combustion cylinders only to said other of said pair of blocks; a pair of countermoving free pistons mounted in each of said combustion cylinders, each of said pistons having a compressor piston portion reciprocable in the associated compressor cylinder and dividing the associated compressor cylinder into dependently variable compressor and bounce chambers; and means for each of said air receiver chambers to cyclically pass compressed fluid from the compresor chambers of a parallel pair of compressor cylinders to the air receiver chamber of the same block. 7

8. In an internal combustion engine: a pair of parallel combustion cylinders; a pair of compression cylinder blocks each of which receives an end of both of said combustion cylinders and each of which is internally divided into an air receiver chamber and a parallel pair of compressor cylinders coaxial with said pair of combustion cylinders; a pair of countermoving free pistons mounted in each of said combustion cylinders, each of said pistons having a compressor piston portion reciprocable in the associated compressor cylinder and dividing the associated compressor cylinder into dependently variable compressor and bounce chambers; means for each of said air receiver chambers to cyclically pass compressed fluid from the compressor chambers of a parallel pair of compressor cylinders to the air receiver chamber of the same block; a cylinder head for each of said compressor cylinder blocks, each of said cylinder heads defining the outer ends of said parallel pair of compressor cylinders and rigidly supporting outer ends of a parallel pair of piston guides coaxially with the associated pair of said free pistons, each of said pistons being telescopically and reciprocably slidable over one of said guides; and conduit means adapted to cyclically equalize fluid pressures in the pair of said bounce chambers for each of said combustion cylinders, said conduit means including a fluid passage extending axially in each of said guides and terminating at an inner end in a port communicating with one of said bounce chambers, said port being cyclically opened and closed by the reciprocation of one of said pistons over said guides.

9. An internal combustion engine as set forth in claim 8 in which the air receiver chambers of said pair of blocks have fluid pressure communication and a valve means is interposed between and operatively associated with said air receiver chambers and said conduit means for said bounce chambers, said valve means being selectively controllable to pass higher fluid pressure from said air receiver chambers to increase fluid pressures in said bounce chambers and, alternatively, to vent said bounce chambers to reduce fluid pressure.

10. In an internal combustion engine: a combustion cylinder; a hollow piston having a head reciprocable in a combustion chamber of said cylinder; a piston guide to reciprocably slidably support the end of said piston opposite said head; and means in said piston and guide to pump a fluid through said guide and into said hollow piston, and actuated by reciprocation of said piston, said guide having fluid inlet and outlet means in a circuit including a source of said fluid.

7 11. In an internal combustion engine: a combustion cylinder; a hollow piston having a head reciprocable in a combustion chamber of said cylinder; a piston guide over which said piston is telescopically reciprocably slidable and having a pump chamber with a fluid inlet passage; and a single-acting pump means carried within said piston to be reciprocated within said pump chamber by reciprocation of said piston whereby said pump means is actuated, said pump means transferring a fluid from said pump chamber to the interior of said hollow piston, said guide having a fluid outlet passage communicating with the interior of said hollow piston.

12. In an internal combustion engine: a combustion cylinder; a hollow power piston having a head reciprocable in a combustion chamber of said cylinder; a hollow piston guide having an open end over which the open end of a skirt portion of said power piston is telescopically received for reciprocable slidable movement on said guide; and oil inlet passage formed through the other end of said guide; check valve means within said guide at said other end of said guide to admit oil from said inlet passage into said guide; a tubular rod connected to said head of said power piston and extending rearwardly within said skirt of said piston; a pump piston afiixed to the rear end of said rod for reciprocation within said guide concurrently with reciprocation of said power piston whereby said check valve means is caused to open during a compression stroke of said power piston to draw oil into said hollow guide; a check valve means in said pump piston to prevent entry of oil into said tubular rod during said compression stroke and adapted to open during a power stroke of said power piston in response to the pressure of oil within said guide between said pump piston and said check valve means of said guide, whereby oil is pumped into said tubular rod to escape through a plurality of orifices formed in said rod immediately behind said piston head; and an oil outlet passage formed in said guide to receive oil from the space between said piston head and said pump piston.

13. An internal combustion engine as set forth in claim 12 in which said check valve means in said pump piston comprises a tubular plunger reciprocably slidably mounted within said rod and a spring means biasing one end of said plunger into sealing engagement with a nose of said pump piston, said nose having a plurality of ports to pass oil from within said guide into an annulus defined between the exterior of said plunger and the interior of said rod, said plunger having an external circumferentially extending shoulder closing the end of said annulus remote from said ports to move said end of said plunger out of said sealing engagement with said nose when oil pressure on said shoulder exceeds the force of said spring means.

14. An internal combustion engine as set forth in claim 13 in which said rod is formed with a plurality of relief ports having fluid communication with said oil outlet passage throughout the range of reciprocation of said pump piston, said spring means yielding further in response to an excessive fluid pressure impressed on said shoulder to 13 permit movement of said plunger until said annulus also has fluid communication with said relief ports, whereby oil can flow from within said guide through said annulus and out of said relief ports to escape to said oil outlet passage without entering into said tubular rod.

References Cited in the file of this patent UNITED STATES PATENTS 14 Kilchenmann Aug. 12, Spier Mar. 23, Wallace Dec. 11, Hub-er July 1 4, Smith June 24, Sakraida et al Apr. 7,

FOREIGN PATENTS Great Britain Mar. 3 1, Great Britain June 11, 

1. IN AN INTERNAL COMBUSTION ENGINE: A COMBUSTION CYLINDER, A PAIR OF COMPRESSOR CYLINDERS COAXIALLY DISPOSED AT OPPOSITE ENDS OF SAID COMBUSTION CYLINDER; A PAIR OF FREE PISTONS MOUNTED IN SAID COMBUSTION CYLINDER FOR OPPOSED RECIPROCATION, EACH OF SAID PISTONS HAVING A COMPRESSOR PISTON PORTION RECIPROCABLE IN THE ASSOCIATED COMPRESSOR CYLINDER AND DIVIDING THE ASSOCIATED COMPRESSOR CYLINDER INTO DEPENDENTLY VARIABLE COMPRESSOR AND BOUNCE CHAMBERS; MEANS TO CYCLICALLY EQUALIZE FLUID PRESSURES IN THE PAIR OF BOUNCE CHAMBERS OF SAID COMBUSTION CYLINDER; AND MEANS INCLUDING SAID COMPRESSOR CHAMBERS FOR CYCLICALLY INGESTING FLUID COMPRESSED IN SAID COMPRESSOR CHAMBERS INTO SAID COMBUSTION CYLINDER. 